Single inductor multi-output buck-boost converter and control method thereof

ABSTRACT

A converter can include: (i) a first switch having a first terminal for receiving an input voltage, and a second terminal coupled to a first terminal of a second switch; (ii) an inductor having a first terminal coupled to a common node of the first and second switches, and a second terminal coupled to a first terminal of a third switch, where second terminals of the second and third switches are coupled to ground; and (iii) a plurality of output channels coupled to a common node of the inductor and the third switch, where the converter operates in a buck-boost mode, a buck mode, or a boost mode based on the relationship between the input voltage and output voltages of the plurality of output channels.

RELATED APPLICATIONS

This application claims the benefit of Chinese Patent Application No.201510435157.1, filed on Jul. 22, 2015, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of the powerelectronics, and more particularly to single inductor multi-outputbuck-boost converters and associated control methods.

BACKGROUND

In a power management integrated circuit, a plurality of output voltagesare typically used in order to supply power to corresponding modules.For example, both the central processing unit (CPU) and display screenmay be powered in a cellphone, and different modules can have differentsupply voltage requirements. Therefore, multiple converter outputs canbe used to satisfy the application requirements. That is, multiplevoltage conversion circuits may be used to satisfy such requirementssince one voltage conversion circuit typically only has one output.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of an example buck-type singleinductor multi-output circuit.

FIG. 2 is a schematic block diagram of an example boost-type singleinductor multi-output circuit.

FIG. 3 is a schematic block diagram of an example multi-outputbuck-boost circuit with a single inductor, in accordance withembodiments of the present invention.

FIG. 4 is a more detailed schematic block diagram of an examplemulti-output buck-boost circuit with a single inductor, in accordancewith embodiments of the present invention.

FIG. 5 is a waveform diagram of example operation of a multi-outputbuck-boost circuit with a single inductor, in accordance withembodiments of the present invention.

DETAILED DESCRIPTION

Reference may now be made in detail to particular embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention may be described in conjunction with thepreferred embodiments, it may be understood that they are not intendedto limit the invention to these embodiments. On the contrary, theinvention is intended to cover alternatives, modifications andequivalents that may be included within the spirit and scope of theinvention as defined by the appended claims. Furthermore, in thefollowing detailed description of the present invention, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. However, it may be readilyapparent to one skilled in the art that the present invention may bepracticed without these specific details. In other instances, well-knownmethods, procedures, processes, components, structures, and circuitshave not been described in detail so as not to unnecessarily obscureaspects of the present invention.

FIGS. 1 and 2 show example single inductor multi-output circuits havingtwo types: buck-type and boost-type. Referring now to FIG. 1, shown is aschematic block diagram of an example buck-type single inductormulti-output circuit. This example circuit can include input voltageVin, main power switch Q1 and rectifying switch Q2 that are alternatelyturned on, and switches Q3, Q4, and Q5 that are respectively used tocontrol corresponding output channels (e.g., OUT1, OUT2, and OUT3).However, in such a circuit, at least one output channel should have anoutput voltage that is lower than an input voltage, and a conductiontime that is longer than a predetermined time during each switchingcycle, in order to avoid abnormal operation due to the inductor notbeing able to sufficiently store energy.

Referring now to FIG. 2, shown is a schematic block diagram of anexample boost-type single inductor multi-output circuit. This examplecircuit can include input voltage Vin, main power switch Q1 fortransmitting energy to inductor L in a conduction state, and switchesQ2, Q3, and Q4 that are respectively used to control correspondingoutput channels (e.g., OUT1, OUT2, and OUT3), for transmitting energystored in inductor L thereto. However, in such a circuit, at least oneoutput channel should have an output voltage that is higher than aninput voltage, and a conduction time to be longer than a predeterminedtime during each switching cycle, in order to avoid the inductor currentnot being reset.

In one embodiment, a converter can include: (i) a first switch having afirst terminal for receiving an input voltage, and a second terminalcoupled to a first terminal of a second switch; (ii) an inductor havinga first terminal coupled to a common node of the first and secondswitches, and a second terminal coupled to a first terminal of a thirdswitch, where second terminals of the second and third switches arecoupled to ground; and (iii) a plurality of output channels coupled to acommon node of the inductor and the third switch, where the converteroperates in a buck-boost mode, a buck mode, or a boost mode based on therelationship between the input voltage and output voltages of theplurality of output channels. In addition, a method of controlling theconverter can include: (i) determining whether the converter operates ina buck-boost mode, a buck mode, or a boost mode based on therelationship between the input voltage and output voltages of theplurality of output channels; and (ii) controlling the first, second,and third switches in response to the determined mode of operation and aswitching cycle of the converter.

Referring now to FIG. 3, shown is a schematic block diagram of anexample multi-output buck-boost circuit with a single inductor, inaccordance with embodiments of the present invention. In this particularexample, the converter can include switches Q1, Q2, and Q3, inductor L,and a plurality of output terminals. Each output terminal can connect toa switch for turning on and off the corresponding channel. In thisexample, there are three output terminals (e.g., OUT1, OUT2, and OUT3),but more or fewer than three output terminals can also be supported inparticular embodiments. Switch Q1 has a first terminal for receivinginput voltage Vin, and a second terminal that can connect to a firstterminal of switch Q2. A common node of switches Q1 and Q2 can connectto a first terminal of inductor L, and a second terminal of inductor Lcan connect to a first terminal of switch Q3. Second terminals ofswitches Q2 and Q3 can connect to ground, and a common node of inductorL and switch Q3 can be coupled to the plurality of output terminals.

In particular embodiments, a single inductor multi-output circuitoperating in a buck-boost mode may have three operation stages within agiven switching cycle. In operation stage 1, both of switches Q1 and Q3may be on switch Q2 may be off, inductor L can receive energy from inputvoltage Vin, and the plurality of output channels can all be off. Inoperation stage 2, switch Q1 can be on, switches Q2 and Q3 may be off,energy may be transmitted from input voltage Vin to the plurality ofoutput channels, and the output channels can be sequentially turned onone by one. In operation stage 3, switches Q1 and Q3 may be off, switchQ2 may be on, and the output channels can be turned on one by one untilthe switching cycle ends. Thus, the plurality of output channels can be(e.g., sequentially) turned on one by one during the second and thirdoperation stages, and the last output channel can remain on until theswitching cycle ends.

The converter can also operate in other modes, as opposed to thebuck-boost mode whereby some output channels have a larger outputvoltage than the input voltage, and other output channels have a smalleroutput voltage than input voltage. For example, the converter canoperate in a buck mode or a boost mode whereby the input voltage iseither larger than all of the output voltages, or smaller than all ofthe output voltages. The operation mode of the converter can thus bedetermined based on the relationship between the input voltage and theoutput voltages, such as including considerations of applicationrequirements (e.g., output voltage levels for CPU, display, etc.).

In the buck mode, when input voltage Vin is relatively large (e.g.,larger than all output voltages), and during a first portion of theswitching cycle, switch Q3 can be off, switch Q1 can be turned on todirectly transmit energy to the output channels, and the plurality ofoutput channels can be turned on in sequential fashion (e.g., one byone). Then, during a second portion of the switching cycle, switch Q1can be turned off, and switch Q2 can be turned on (e.g., as afree-wheeling diode).

In the boost mode, when input voltage Vin is relatively small (e.g.,input voltage Vin is smaller than all output voltages), and during afirst portion of the switching cycle, switch Q2 can be off, switches Q1and Q3 can be turned on to transmit energy from input voltage Vin toinductor L, and all the output channels may be off. Then, during asecond portion of the switching cycle, switch Q3 can be turned off totransmit energy from input voltage Vin to the plurality of outputchannels, and the output channels can be turned on in sequential fashion(e.g., one by one).

Referring now to FIG. 4, shown is a more detailed schematic blockdiagram of an example multi-output buck-boost circuit with a singleinductor, in accordance with embodiments of the present invention. Inthis particular example, sawtooth signal Q1_RAMP can be compared againstreference signal Vref1 to generate control signals for turning on/offswitches Q1 and Q2. For example, control signal Q1_ON can be used tocontrol switch Q1, and control signal Q2_ON obtained by invertingcontrol signal Q1_ON can be used to control switch Q2. Ramp wave signalQ1_RAMP may also be compared against reference signal Vref2 to generatecontrol signal Q3_ON for turning on/off switch Q3. In addition, currentsense signal I_(SEN) _(_) _(Q1) obtained by sampling the inductorcurrent can be superimposed with sawtooth wave signal Q1_RAMP, and mayfurther be respectively compared against reference signals Vref1 andVref2.

By inverting control signal Q3_ON of switch Q3, control signal Q3_OFFcan be used for turning on channel OUT1. In order to obtain controlsignal Q4_OFF for turning off channel OUT1, output voltage feedbacksignal FB1 can be obtained by sampling output voltage V_(OUT1) ofchannel OUT1. Feedback compensation signal VC1 can be obtained bycomparing output voltage feedback signal FB1 against correspondingreference voltage VF1, and compensating a difference therebetween viacompensation module Zs. Also, current sense signal I_(SEN) _(_) _(Q4)can be obtained by sampling an output current of channel OUT1, and thatit may be superimposed with corresponding sawtooth wave signal Q4_RAMP,and further compared against feedback compensation signal VC1, togenerate control signal Q4_OFF.

After completing the turning on and off procedure of the first channel,the first channel can be turned off, and the second channel can begin tobe turned on at substantially the same time. That is, the latter channelcan be substantially simultaneously turned on when the former channel isturned off, so the control signal for turning off the former channel canbe used as the control signal for turning on the current channel. Inorder to turn off the current channel, a feedback compensation signalmay be obtained by sampling and compensating an output voltage of thecurrent channel, and an output current of the current channel can besampled and further superimposed with a corresponding sawtooth wavesignal, to be compared against the feedback compensation signal forturning off the current channel.

In this example, OUT2 can be described as the “current” channel, andOUT1 may be described as the “former” channel, and accordingly theremaining channels can be controlled as described above. Thus the lastchannel can be turned on by the control signal that is used to turn offthe former channel. In this example, fixed-frequency control may beemployed with a clock signal “Clock” to turn off the last channel at theend of the switching cycle, which may be the last channel simultaneouslyturned off when the on time of the clock signal completes. It is to beunderstood that the control is not limited to fixed frequency, such asby adjusting the time length of high level or low level of the clocksignal.

Referring now to FIG. 5, shown is a waveform diagram of exampleoperation of a multi-output buck-boost circuit with a single inductor,in accordance with embodiments of the present invention. This diagramshows the operation states, on time and off time of switches, and thewaveform of the inductor current, where I denotes the inductor current,and Q1, Q2, Q3, Q4, Q5, and Q6 represent the on time intervals ofcorresponding switches. FIG. 5 also shows the relationship betweensawtooth wave signal Q1_RAMP and reference signals Vref1 and Vref2. Forexample, the difference between reference signals Vref1 and Vref2 issmaller than the peak to peak value of sawtooth wave signal Q1_RAMP.Reference signal Vref1 may be smaller than the peak value of sawtoothwave signal Q1_RAMP, and reference signal Vref2 can be larger than thevalley value of sawtooth wave signal Q1_RAMP. Reference signal Vref1 maybe determined according to output voltages of a plurality of outputchannels. For example, Vref1=K1*Vc1+ K2*Vc2+ K3*Vc3, where coefficient Kmay be adjusted according to the importance or priority of differentchannels.

The embodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with modifications as are suited to particularuse(s) contemplated. It is intended that the scope of the invention bedefined by the claims appended hereto and their equivalents.

What is claimed is:
 1. A converter, comprising: a) a first switch havinga first terminal for receiving an input voltage, and a second terminalcoupled to a first terminal of a second switch; b) an inductor having afirst terminal coupled to a common node of said first and secondswitches, and a second terminal coupled to a first terminal of a thirdswitch, wherein second terminals of said second and third switches arecoupled to ground; c) a first comparator configured to generate a firstcontrol signal for controlling said first and second switches bycomparing a first reference signal against a superimposition of asawtooth wave signal and an inductor current sense signal; d) a secondcomparator configured to generate a second control signal forcontrolling said third switch by comparing a second reference signalagainst said superimposition of said sawtooth wave signal and saidinductor current sense signal; and e) a plurality of output channelscoupled to a common node of said inductor and said third switch, whereinsaid converter operates in a buck-boost mode, a buck mode, or a boostmode based on the relationship between said input voltage and outputvoltages of said plurality of output channels, wherein said firstreference signal is determined according to said output voltages andcoefficients of each of said plurality of output channels, and whereinsaid coefficients are adjusted according to a priority of each of saidplurality of output channels.
 2. The converter of claim 1, wherein whensaid converter operates in a buck-boost mode, said first and thirdswitches are turned on and said inductor receives energy from said inputvoltage during a first operation stage of a switching cycle of saidconverter, said third switch is turned off and said plurality of saidoutput channels are sequentially turned on during a second operationstage of said switching cycle, and said first switch is turned off, saidsecond switch is turned on, and said plurality of said output channelsare sequentially turned on during a third operation stage of saidswitching cycle.
 3. The converter of claim 2, configured to becontrolled in a fixed frequency, and wherein a last channel remains onuntil said switching cycle is completed.
 4. The converter of claim 1,wherein when said converter operates in a buck mode, said third switchis off, said first switch is turned on to transmit energy to saidplurality of output channels, and said plurality of output channels aresequentially turned on during a first portion of a switching cycle ofsaid converter, and said second switch is turned on as a free-wheelingdiode during a second portion of said switching cycle.
 5. The converterof claim 1, wherein when said converter operates in a boost mode, saidsecond switch is off, said first and third switches are turned on totransmit energy from said input voltage to said inductor, and each ofsaid plurality of output channels are turned off during a first portionof a switching cycle of said converter, and said third switch is turnedoff to transmit energy from said input voltage to said plurality ofoutput channels, and said plurality of output channels are sequentiallyturned on during a second portion of said switching cycle.
 6. Theconverter of claim 1, wherein a difference between said first and secondreference signals is less than a peak to peak value of said sawtoothwave signal.
 7. The converter of claim 6, wherein: a) said controlsignal for controlling said third switch is inversed to control the turnon of a first output channel of said plurality of output channels; b) afeedback compensation signal is obtained by sampling and compensating anoutput voltage of said first channel; and c) an output current sensesignal is superimposed on a corresponding sawtooth wave signal, andfurther compared against said feedback compensation signal to controlthe turn off of said first output channel.
 8. The converter of claim 7,wherein: a) after completing the turn on and turn off of said firstoutput channel, a latter channel is simultaneously turned on when aformer channel is turned off; b) in order to turn off said latterchannel, an output voltage of said latter channel is sampled andcompensated to obtain a corresponding feedback compensation signal; andc) an output current sense signal of said latter channel is superimposedon a corresponding sawtooth wave signal and further compared againstsaid feedback compensation signal to control the turn off of said latterchannel.
 9. The converter of claim 1, wherein said inductor currentsense signal is obtained by sampling a current through said inductor.10. The converter of claim 1, wherein said first reference signal issmaller than the peak value of said sawtooth wave signal, and saidsecond reference signal is larger than the valley value of said sawtoothwave signal.
 11. A method of controlling a converter, wherein saidconverter comprises a first switch, a second switch, a first switchhaving a first terminal for receiving an input voltage, and a secondterminal coupled to a first terminal of a second switch, an inductorhaving a first terminal coupled to a common node of said first andsecond switches, and a second terminal coupled to a first terminal of athird switch, wherein second terminals of said second and third switchesare coupled to ground, and a plurality of output channels coupled to acommon node of said inductor and said third switch, the methodcomprising: a) determining whether said converter operates in abuck-boost mode, a buck mode, or a boost mode based on the relationshipbetween said input voltage and output voltages of said plurality ofoutput channels; b) generating a first control signal for controllingsaid first and second switches by comparing a first reference signalagainst a superimposition of a sawtooth wave signal and an inductorcurrent sense signal; c) generating a second control signal forcontrolling said third switch by comparing a second reference signalagainst said superimposition of said sawtooth wave signal and saidinductor current sense signal; and d) controlling said first, second,and third switches in response to said determined mode of operation anda switching cycle of said converter, wherein said first reference signalis determined according to said output voltages and coefficients of eachof said plurality of output channels, and wherein said coefficients areadjusted according to a priority of each of said plurality of outputchannels.
 12. The method of claim 11, further comprising when saidconverter operates in a buck-boost mode: a) turning on said first andthird switches such that said inductor receives energy from said inputvoltage during a first operation stage of said switching cycle; b)turning off said third switch and sequentially turning on said pluralityof said output channels during a second operation stage of saidswitching cycle; and c) turning off said first switch, turning on saidsecond switch, and sequentially turning on said plurality of said outputchannels during a third operation stage of said switching cycle.
 13. Themethod of claim 12, further comprising controlling said converter in afixed frequency, wherein a last channel remains on until said switchingcycle is completed.
 14. The method of claim 11, further comprising whensaid converter operates in a buck mode: a) turning off said thirdswitch, turning on said first switch to transmit energy to saidplurality of output channels, and sequentially turning on said pluralityof output channels during a first portion of said switching cycle; andb) turning on said second switch as a free-wheeling diode during asecond portion of said switching cycle.
 15. The method of claim 11,further comprising when said converter operates in a boost mode: a)turning off said second switch , turning on said first and thirdswitches to transmit energy from said input voltage to said inductor,and turning off each of said plurality of output channels are turned offduring a first portion of said switching cycle; and b) turning off saidthird switch to transmit energy from said input voltage to saidplurality of output channels, and sequentially turning on said pluralityof output channels during a second portion of said switching cycle. 16.The method of claim 11, wherein a difference between said first andsecond reference signals is less than a peak to peak value of saidsawtooth wave signal.
 17. The method of claim 16, further comprising: a)inverting said control signal for controlling said third switch tocontrol the turn on of a first output channel of said plurality ofoutput channels; b) generating a feedback compensation signal bysampling and compensating an output voltage of said first outputchannel; and c) superimposing an output current sense signal on acorresponding sawtooth wave signal, and further comparing against saidfeedback compensation signal to control the turn off of said firstoutput channel.
 18. The method of claim 17, further comprising: a) aftercompleting the turn on and turn off of said first output channel,simultaneously turning on a latter channel when a former channel isturned off; b) generating a corresponding feedback compensation signalby sampling and compensating an output voltage of said latter channel inorder to turn off said latter channel; and c) controlling the turn offof said latter channel by superimposing an output current sense signalof said latter channel on a corresponding sawtooth wave signal andfurther comparing against said feedback compensation signal.
 19. Themethod of claim 11, further comprising obtaining said inductor currentsense signal by sampling a current through said inductor.
 20. The methodof claim 11, wherein said first reference signal is smaller than thepeak value of said sawtooth wave signal, and said second referencesignal is larger than the valley value of said sawtooth wave signal.